In recent years, with a growing consciousness of and a growing interest in environmental issues such as global warming, reduction of carbon dioxide emissions and reduction of a concentration of carbon dioxide in air by fixation of carbon dioxide have been great challenges. Therefore, attempts to break dependence on fossil fuels and to actively utilize a biomass, which is a carbon neutral source, as an energy source have been made actively.
For example, Euglena is known as an alga producing a lipid or the like in the cells. With focusing attention on lipid productivity thereof, there has been proposed a method involving: culturing Euglena aerobically; then placing the resultant under an anaerobic condition to convert a storage polysaccharide paramylon into a wax ester; physically breaking the resultant; and then isolating the wax ester by centrifugation, solvent extraction or the like (Patent Document 1). Further, there is known a method involving: heating and pressurizing Euglena using an autoclave; allowing a high concentration of a protease to act on the Euglena; and fractionating a water-soluble component by filtration. However, fractionation of a water-insoluble component has not been examined (Patent Document 2).